Pre-/analytical factors affecting whole blood and plasma glucose concentrations in loggerhead sea turtles (Caretta caretta)

Abstract

Blood glucose is vital for many physiological pathways and can be quantified by clinical chemistry analyzers and in-house point-of-care (POC) devices. Pre-analytical and analytical factors can influence blood glucose measurements. This project aimed to investigate preanalytical factors on whole blood and plasma glucose measurements in loggerhead sea turtles (Caretta caretta) by evaluating the effects of storage (refrigeration) up to 48h after sampling and of packed cell volume (PCV) on whole blood glucose analysis by POC glucometer (time series n = 13); and by evaluating the effects of storage (room temperature and refrigeration) on plasma glucose concentrations using a dry slide chemistry analyzer (DCA) at various conditions: immediate processing and delayed plasma separation from erythrocytes at 24h and 48h (time series n = 14). The POC glucometer had overall strong agreement with the DCA (CCC = 0.76, r = 0.84, C b = 0.90), but consistently overestimated glucose concentrations (mean difference: +0.4 mmol/L). The POC glucometer results decreased significantly over time, resulting in a substantial decline within the first 2h (0.41±0.47 mmol/L; 8 ±9%) that could potentially alter clinical decisions, thereby highlighting the need for immediate analysis using this method. The effects of PCV on glucose could not be assessed, as the statistical significance was associated with one outlier. Storage method significantly affected plasma glucose measurements using DCA, with room temperature samples resulting in rapid decreases of 3.57±0.89 mmol/L (77±9%) over the first 48h, while refrigerated samples provided consistent plasma glucose results over the same time period (decrease of 0.26±0.23 mmol/L; 6±5%). The results from this study provide new insights into optimal blood sample handling and processing for glucose analysis in sea turtles, show the suitability of the POC glucometer as a rapid diagnostic test, and confirm the reliability of plasma glucose measurements using refrigeration. These findings emphasize the need to consider pre-/analytical factors when interpreting blood glucose results from loggerhead sea turtles.

Comparison of 2 glucose analytical methodologies in immature Kemp’s ridley sea turtles: dry chemistry of plasma versus point-of-care glucometer analysis of whole blood

“…Similar to other studies, the POC glucometer produced significantly higher concentrations (by 1.4 mmol/L in our study) compared to DCA results. 16,22,27,31 The 2 methods were strongly correlated; however, 25 of 33 (76%) and 8 of 33 (24%) samples had a ≥ 10% and ≥ 40% difference between the methodologies, respectively. Hence, this brand of glucometer consistently produced results that were above the total allowable error of 10% for glucose set by the American Society for Veterinary Clinical Pathology, 13 which raises concern that this bias may affect clinical decisions.…”

“…24 Plasma or serum glucose analysis by standard chemistry analyzers is considered the gold standard compared to glucometers; however, laboratory chemistry analyses come at increased costs with longer turnaround times. 10,15 POC glucometers using combined glucose oxidase and potentiometry have been validated for use in 2 sea turtle species (green sea turtles, Chelonia mydas ; loggerhead turtles, Caretta caretta ) 16,22 ; however, method comparison and validation have not yet been reported in Kemp’s ridley sea turtles (syn. Atlantic ridley; Lepidochelys kempii ).…”

“…11 Glucometer analysis of whole blood in sea turtles has shown a slight positive bias in comparison to plasma analysis by dry chemistry analysis (DCA). 16,22 Therefore, for free-ranging, immature Kemp’s ridley sea turtles from Georgia, USA, our objectives were to 1) compare glucose concentrations using 2 different analytical methods: DCA using plasma and POC glucometer using whole blood; 2) determine the impact of packed cell volume (PCV) on glucometer measurements; and 3) establish reference intervals (RIs) for the glucometer.…”

“…Previous studies on glucose comparisons using DCA and POC glucometers have been conducted in green and loggerhead sea turtles. 16,22 The glucometer brand that we used is different from the one employed in those studies 16,22 ; however, both brands use the same electrochemical-based methodology with glucose oxidase and potentiometry versus other optical methodology-based glucometers. Glucose consumption by RBCs continues after blood collection, and concentrations have been shown to rapidly decrease with delayed plasma separation times and sample exposure to increased temperatures.…”

“…Glucose consumption by RBCs continues after blood collection, and concentrations have been shown to rapidly decrease with delayed plasma separation times and sample exposure to increased temperatures. 7,16 Because our samples were processed immediately (i.e., within 5 min of collection), we can assume that our glucose measurements, both by DCA and glucometer, were not affected by continued RBC consumption.…”